Numerous devices, including without limitation personal audio devices, wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, often use one or more ramp generation circuits. In operation, such ramp generation circuits produce a periodic signal that, during each periodic cycle, ramps from a minimum magnitude (e.g., zero) to a maximum magnitude. In some instances, a ramp signal generated by a ramp-generation circuit may be used by a pulse-width modulator to generate a pulse-width modulated signal, as is known in the art.
FIG. 1 depicts an example ramp-generation circuit 100, as is known in the art. As shown in FIG. 1, ramp-generation circuit 100 may include a reference-current generation subcircuit 102 for generating a reference current Iref=Vref/Rtrim, where Vref is a reference voltage and Rtrim is a resistance of a resistor 104 of reference-current generation subcircuit 102. Ramp-generation circuit 100 may also include a current-mirror stage 106 that sources an amplifier input current proportional to reference current Iref to a positive input terminal of output amplifier stage 108 and sinks an amplifier input current of identical magnitude from a negative input terminal of output amplifier stage 108. Such amplifier input currents may flow through feedback capacitors 110 of equal capacitance, integrating charge during each cycle of ramp-generation circuit 100 to generate, at each output terminal of output amplifier stage 108, a sawtooth ramp signal, which is reset to its minimum voltage (e.g., zero) during each cycle boundary of ramp-generation circuit 100 as a result of periodic activation of switches 112 by clock signal CLK.
Ramp-generation circuit 100 of FIG. 1 may have numerous disadvantages. For example, in the topology of FIG. 1, reference voltage Vref is converted into reference current Iref that is mirrored through current-mirror stage 106 to generate push-pull reference current sources to be integrated on feedback capacitors 110, which provide a voltage-domain output. Therefore, the topology of FIG. 1 has a voltage-to-current conversion, generation of push-pull currents, and then current-to-voltage conversion. These multiple conversion steps may add significant error in ramp generation, especially error due to process, voltage, temperature, and component mismatch. Thus, ramp-generation circuit 100 may also be unable to track changes in process, frequency, temperature, and/or supply voltage. As another example, the resistance Rtrim of resistor 104 may require trimming to account for process variations of ramp-generation circuit 100, which adds cost and design complexity to ramp-generation circuit 100. In addition, as is the case in any circuit, it may be desirable to provide similar functionality to ramp-generation circuit 100 but with fewer electrical and electronic components, in order to minimize circuit size and/or power consumption.